1. Field of the Invention
The present invention relates to a surface-mount type antenna which is a compact antenna, and an antenna apparatus for use in mobile communication apparatus such as a cellular phone.
2. Description of the Related Art
Recently, in keeping with rapid advancement of down-sized, lightweight, and high-performance mobile communication equipment such as a cellular phone, miniaturization and high performance have come to be increasingly demanded of an antenna which constitutes such equipment. To meet such demands, for example, a surface-mount type antenna has hitherto been developed.
Now, a surface-mount type antenna of conventional design and an antenna apparatus incorporating the antenna will be described with reference to a perspective view shown in FIG. 10.
In FIG. 10, reference numeral 200 represents a surface-mount type antenna. The surface-mount type antenna 200 is mounted on a mounting substrate 210, thus constituting an antenna apparatus 220. In the surface-mount type antenna 200 shown in FIG. 10, reference numeral 201 represents a substantially rectangular parallelepiped base body; reference numeral 202 represents a feeding terminal; reference numeral 206 represents an auxiliary terminal for surface mounting; and reference numerals 203, 204, and 205 each represent a radiating electrode. Strictly speaking, The conductors of the individual radiating electrode portions are conjoined to one another to constitute the radiating electrode. Moreover, in the mounting substrate 210, reference numeral 211 represents a substrate; reference numeral 207 represents a feeding electrode; reference numeral 208 represents an auxiliary electrode for surface mounting; and reference numeral 209 represents a ground conductor layer.
In the conventional surface-mount type antenna 200, the feeding terminal 202 is formed on a side surface a of the base body 201. The radiating electrode 203, 204, 205, which is routed as a long conductor pattern, is configured such that its end extends upwardly from the feeding terminal 202 on the side surface a, is then substantially U-shaped, as viewed plane-wise, on a top surface b of the base body 201, and is eventually formed into an open end. The open end of the radiating electrode 205 extends along the shorter side (the right-hand side of the top surface b of the base body 201 in FIG. 10) of the base body 201.
The open end 205 of the radiating electrode, which extends along the shorter side (the right-hand side of the top surface b of the base body 201 in FIG. 10) of the base body 201, may be cut down for the purpose of adjusting the resonant frequency to a desired level. By making the radiating electrode shorter in this way, the resonant frequency can be increased.
Moreover, in the surface-mount type antenna, to achieve impedance matching between the radiating electrode 203, 204, 205 and the feeding electrode 207, a matching circuit (not shown) is additionally disposed in the feeding electrode 207 of the mounting substrate 210 that is connected to the feeding terminal 202 of the radiating electrode 203, 204, 205.
Meanwhile, in the mounting substrate 210, on the top surface of the substrate 211 are arranged the feeding electrode 207, the auxiliary electrode for surface mounting 208, and the ground conductor layer 209. The ground conductor layer 209 is arranged face to face with one side of the auxiliary electrode for surface mounting 208 and has connection with the auxiliary electrode for surface mounting 208.
Then, the surface-mount type antenna 200 is mounted on the top surface of the mounting substrate 210, with the feeding terminal 202 connected to the feeding electrode 207, and the auxiliary terminal for surface mounting 206 connected to the auxiliary electrode for surface mounting 208. Thereupon, the antenna apparatus 220 is realized.
A related art is disclosed in Japanese Unexamined Patent Publication 2002-158529 (2002).
However, the conventional surface-mount type antenna 200 has the following disadvantage. In the radiating electrode 203, 204, 205, for the purpose of adjusting the resonant frequency to a desired level, the open end 205 of the radiating electrode extending along the shorter side (the right-hand side of the top surface b of the base body 201 in FIG. 10) of the base body 201 of the surface-mount type antenna 200 may be cut down. By making the radiating electrode shorter in this way, the resonant frequency can be increased. In this case, however, the variation of the resonant frequency corresponding to the cut length is so significant that the resonant-frequency adjustment operation becomes difficult. As a result, the desired antenna characteristics as designed cannot be readily attained with stability.